The present invention relates to generating image data, wherein a plurality of elements are defined in three dimensional space.
Several procedures are known for rendering images containing elements defined as three dimensional data. A known approach to generating images of photo-realistic quality is to consider reflections between all elements simultaneously. The light emission of any given element is considered as being dependent upon the sum of contributions from all other elements, and a set of equations is defined that represents these interactions. The light emission values for all the elements are then determined simultaneously by solving the system of equations.
This procedure is known as radiosity simulation. The system of equations is usually extremely large and several refinements to radiosity simulation have been established in order to make implementation of this method practical for scenes containing large numbers of elements.
A known advantage of radiosity is that once the system of equations has been solved and light emission values have been determined, the light emission of elements may be considered as view-independent, resulting in a separate radiosity rendering process which is capable of rendering a view from any position. The high efficiency of radiosity rendering makes radiosity particularly suitable for demanding applications, such as generating long sequences of image data frames for film or video, or generating image data in real time.
In the process of radiosity simulation, the presence of occluding elements may significantly increase the level of computation required to define a system of equations. Establishing a system of equations requires an evaluation is to be made of the amount of light transferred between every possible pair of elements. If an additional element interferes with the transfer of light between a pair of elements, it is said that the receiving element is occluded. Under these circumstances, evaluation of the proportion of light received by the receiving element becomes much more complex than when it can be assumed that there is no occluding element present.
Thus the presence of occlusions can significantly increase the required level of processing in the radiosity simulation procedure, and in many situations considering certain elements as being occluding may result in minimal enhancement to the realism of the synthesized image. Consequently, it is known to selectively ignore some occlusions and then perform a radiosity simulation in which it is assumed that the same quantum of light may reflect off both the occluding and occluded elements. This procedure can reduce the level of computational overhead required during a radiosity simulation. However, as is known, this may also introduce unwanted visual artifacts.
According to a first aspect of the present invention, there is provided a method of generating image data, wherein a plurality of elements are defined in three dimensional space; wherein selected elements are set as being non-occluding; light emission values for said elements are determined by calculating the effect of light reflections between said elements; and an accumulated level of light is adjusted in response to the visibility of elements including at least one of said non-occluding elements.
In a preferred embodiment, the level of light is reduced to be substantially similar to that achieved when said non-occluding elements are occluding.
According to a second aspect of the present invention, there is provided a method of generating image data, wherein a plurality of elements are defined in three dimensional space; wherein selected elements are set as being non-occluding; light emission values for said elements are determined by calculating the effect of light reflections between said elements; and light emission errors resulting from said non-occluding elements are combined with light emission values resulting from other elements.
According to a third aspect of the present invention, there is provided a method of generating image data, wherein a plurality of elements are defined in three dimensional space; wherein selected elements are set as being non-occluding; light emission values for said elements are determined by calculating the effect of light reflections between said elements; and light emission errors resulting from said non-occluding elements are reduced by the steps of: accumulating a brightness value for an element; accumulating a form factor for an element; and normalising said accumulated brightness value in response to said accumulated form factor.